With the popularity of wearables, high-quality wireless communication among a group of devices is becoming increasingly important. Modern wireless technologies include LTE, Wi-Fi, and Bluetooth, to name a few, the developments of which have been driven by needs to eliminate cluttering physical connections and wirings. Earbuds, earphones or headphones allow users to enjoy hand-free audio listening, and may be wirelessly connected to the main device based on the Bluetooth standard, for example. A device based on the Bluetooth standard operates for exchanging data over short distances, at frequencies between 2402 and 2480 MHz, or 2400 and 2483.5 MHz including guard bands 2 MHz wide at the bottom end and 3.5 MHz wide at the top end. This band is commonly called: Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency (RF) band.
In conventional earbuds or earphones, however, high audio quality including stereo effects can be typically achieved by linking the pair by a wired connection having a common controlling box. Such physical wirings are necessitated by the fact that when devices are embedded in skin, the wireless communication signal can fall off along the pathway, making the signal transmission and reception extremely difficult. Skin has both electric and magnetic properties, and it matters if the skin is wet or dry. As a rule of thumb, through 5 mm of skin, a Bluetooth signal will lose 3 decibels (dB) on average. That compares to the loss of 6 dB for a Bluetooth signal going through a standard concrete wall.
In many cases, to keep costs down, wearable devices need to be designed with low-cost off-the shelf antennas without the functional flexibility or efficiency typically provided by a custom antenna that takes advantage of the material and design of the wearable devices. It is estimated that use of custom antennas potentially raises the materials cost in a wearable by 10%-15%, for typical cases. Today, a small off-the-shelf antenna based on copper or ceramic could cost from 30 cents to 60 cents, or even lower, when purchased in bulk.
Thus, it is in users' best interest to have a pair of earbuds or earphones with high-quality and reliable communication based on low-cost antennas and components, and most importantly, without relying on connecting wirings.